What is "tank iron"

Tank \Tank\ (t[a^][ng]k), n. [Pg. tanque, L. stangum a pool; or perhaps of East Indian origin. Cf. Stank, n.]

1. A large basin or cistern; an artificial receptacle for liquids.

2. A pond, pool, or small lake, natural or artificial.

   We stood in the afterglow on the bank of the tank and saw the ducks come home.
   --F. Remington.

   The tanks are full and the grass is high.
   --Lawson.

3. (Mil.) a heavily armored combat vehicle which moves on caterpillar treads, rather than wheels. It typically carries a cannon and a heavy machine, and sometimes other weapons. It is the main distinguishing weapon of an armored division.

4. a jail cell for temporarily holding prisoners, as in a police station.

   Tank engine, a locomotive which carries the water and fuel it requires, thus dispensing with a tender.

   Tank iron, plate iron thinner than boiler plate, and thicker than sheet iron or stovepipe iron.

   Tank worm (Zo["o]l.), a small nematoid worm found in the water tanks of India, supposed by some to be the young of the Guinea worm.

n. plate iron thinner than boilerplate and thicker than sheet iron or stovepipe iron

n. plate iron that is thinner than boilerplate but thicker than sheet iron or stovepipe iron